Horn for loud-speaker



Feb. 9, 1943. P. w. KLIPSCH HORN FDR LOUDSPEAKER Filed Feb. 5, 1940INVENTOR.

Patented Feb. 9, 1943 HORN FOR LOUD-SPEAKER Paul W. Klipsch, Houston,Tex., assignor of twenty per cent to Ray L. Smith, Houston,

Tex.

Application February 5, 1940, Serial No. 317,260

7 Claims.

This invention relates to horn loud-speakers, particularly to the typewherein the horn is curled or folded to shorten its overall dimensionscompared to the axial length of the horn.

It is well established that loud-speakers, in order to reproduce a givenfrequency range, must have dimensions comparable to the longest wavelength corresponding to the lowest frequency in the range. In the caseof horns the rate of flare, the length of horn tube, and the area of themouth opening all must be determined by the wavelengths to bereproduced. It is customary to shorten the outside dimensions of hornsby folding, but even then the dimensions of the mouth opening must belarge if the frequencies to be reproduced include very low frequencies.For residential use the non-directional or flat bafile is usuallyemployed in conjunction with a large conical diaphragm, suchconstructions being suitable from the standpoint of physical size, butpossessing the disadvantage of low efficiency, especially at lowfrequencies. The combination of a folded horn for low frequencyreproduction and a second radiating region for the high frequencies hasbeen proposed and used to some extent for domestic radio and soundsystems. One such arrangement in which the same diaphragm served forboth sources was described by Olson and Hackley in a paper CombinationHorn and Direct Radiator Loud- Speaker, Proc. I. R. E. Dec. 1936, page1557.

It is the object of this invention to provide means forefiicientlyreproducing the lower range of the audio spectrum withacoustic elements of restricted size.

More specifically, it is an object of the present invention to provide aloud-speaker for the lower audio frequency register consisting of a hornor directional baffle which, is folded to reduce its outside dimensions,and in which the walls of a room in which the speaker is to be operatedform a part of the boundaries of the horn tube.

A further object is to provide a horn baflle formed with a series oftubes bounded by rigid walls, the tubes expanding from a throat at asuitable rate of flare, and terminating in a mouth opening ofinsufiicient size to radiate the lowest frequencies whereby the totalsize of the horn unit is satisfactory for use in rooms of ordinary size,the outer walls or bafile of the horn being so arranged that when placedin the corner of a room the walls of the room cooperate with theenclosure to form an additional length of expanding horn terminating ina mouth opening adequate to deliver efliciently sounds of the lowestfrequency it is desired to transmit. Incidentally, the physical size ofthe unit is such that it will go through an average size door, whichmight well be stated as another object of the invention.

These and other objects will be evident from the following descriptiontaken in connection with the illustrations in which:

Fig. 1 is an oblique projection view of a loudspeaker in accordance withthe present invention,

Fig. 2 is a sectional view from the top taken on line A-A Fig. 1 andshowing the baflles constituting the folded horn,

Fig. 3 is a section View from the side taken on line 3-3 Fig. 2 andshowing the arrangement of transducer and throat, and

Fig. 4 is another sectional view from the side taken on line CC Fig. 2and showing the guides or bailles in the next to last section of horn.

While outdoor sound installations are common, the normal environment ofa loudspeaker is a room or hall. The vast public acceptance ofbroadcasting has resulted in an enormous number of loud-speakerssituated in the rooms of residences. Such loud-speakers are designed tobe complete within themselves so that they are suitable for anyenvironment. Since, however, the room is the normal environment, itseems justified to design a loud-speaker for such environment to utilizethe properties of the environment for the improvement of the speakerperformance.

In the present invention, the effect of room walls flaring away from acorner is taken advantage of to complete the length of tube at suitableflare rate of a horn type loud-speaker.

The design shown in the drawing consists of a transducer working intothe throat of an exponentially expanding horn, suitably folded to reducethe overall dimensions. As shown, the structure is too short, and themouth too small for efficient reproduction, but when placed in thecorner of a room, the walls of the room bound an additional fold orsection of the horn completing the horn length and continuing the flareso that the effective mouth opening is brought up to the desired area.The saving in material otherwise required to complete this last fold isobvious, and the reduction in size of the speaker to such dimensionsthat it can be readily manufactured, handled, transported and placed inservice is obviously of considerable value to the user. A furtheradvantage due to wall reflection will later be made apparent.

In Fig. 1 the walls and floor forming the corner of a room also form theoutside of the last' fold of the horn. It will be seen that there aretwo mouths MA and Me in the particular construction shown. The lastsection of horn is bounded by a wall and a bafile 2, and by the floorand a wing-like cover 3. Sound is admitted to this last section of hornthrough the last fold (4 in Fig. 2). The bafile 2 is preferably curvedto give it rigidity, but it may be fiat, as shown by Olson and Massa Acompound horn loudspeaker, Journal of the Acoustical Society of America,July, 1936, pp. 48-52 wherein Fig. 6 shows horns with true exponentialcurves and with straight sides approximating the true curve. Theseauthors state that comparisons indicated very little difference below300 cycles.

Fig. 2 is a sectional view A-A of Fig. 1 and is a view from the topthrough transducer l0,

air chamber II with walls l2 and I3, throat H,

and interior baiiles l5, l6, and IT. The arrows show the direction of awave generated by the transducer as it expands outward through thevarious sections of the horn.

Fig. 3 is a vertical section through BB showing a side elevation of thetransducer, air chamher, and throat. The dotted lines show the bafflesbounding the first section of horn opening up to the left. Baffles and2| lie between and span the space between bafiles l6 and I! of Fig. 2whereby the wave passing from the throat I 4 around the ends of thebaffles l6, as indicated by the arrow 1, is permitted to expand slowlybefore passing around the forward edges of bailies I! as indicated bythe arrow 8.

Fig. 4 is another vertical section, through the part of the horn markedC-C in Fig. 2. Baflies 22 and 23 bound the upper and lower sides of thenext to last section of horn shown in Fig. 2 as being bounded byvertical bafiies l1 and 2 and from which the sound waves travel in thedirection indicated by the arrow 9. The dotted lines in Fig. 4 show theupper and lower bounding baflles of the next preceding section of horn,20 and 2| lying, as already indicated, between baflies l6 and I! in Fig.2.

In order to avoid an unduly large air chamber in the apex of the cornerof the room, the corner bailie l8 (Figs. 1 and 2) is arranged so thesectional area of the horn increases regularly around the fold 4.

An important advantage of the'arrangement shown is that theconstructional dimensions of the loud-speaker are smaller than theactual mouth opening RA+MA, and in addition, the walls and fiopr formreflectors which effectively make the mouth area four times the actualarea. Thus one wall forms an image MA of the actual mouth MA, and thefloor and its image form images MA" and MA' respectively of MA ad MA. Inthe absence of the walls extending outwardly through the mouths of thespeaker, the actual mouth opening would have to be four times as large(in area) to give equivalent performance. Or putting it the other wayabout, the presence of the walls bisecting a virtual or efiective mouthleaves only one fourth as large a mouth opening,

United States Patent 2,135,610 wherein the pres-' ence of the ceilingproduces an image and increases the eflective heighth of the mouth.

The cut-off frequency of a horn is determined by the rate of flare ofthe horn and the area of the mouth opening. The diameter of the mouthopening must be larger than about A; or wave length in order to transferthe wave efliciently from the horn to free space. If-the mouth i notcircular, the diameter of a circle having the mouth area may be used todetermine the cut-off due to mouth size.

One design for a speaker of the type disclosed here consists of thefollowing constants:

Table Flare constant in the exponential equation defining the horn areaA in terms of the throat area Ao, A=Ane where a: is the horn lengthexpressed in Diameter of equivalent circle having an area equal to theeffective mouth area inches 86 Frequency at which equivalent diameter ofmouth is wave length cycles '73 The front panel i of Fig. 1 for such adesign need be only 28 inches wide and 48 inches high, dimensions ofsuch order that the unit may be readily transported and will clear theaverage dwelling door. Wings 3 of Fig. 1 may be dismounted fortransport.

Such a design involves dimensions at the curved parts of the passagewaysconnecting the various folds which preclude good performance above about1500 cycles. For this reason, the transducer I0 is arranged to radiatethe high frequencies from its front surface, while the low frequenciesare delivered from the rear surface to the throat to be ultimatelyradiated from the horn mouth. The transducer is a conical diaphragm, thefront of which is open to space and the back of which is loaded by thethroat of the horn. The design of the elements and the selection of across-over frequency from high frequency front radiation to lowfrequency horn operation is discussed by Olson et. al., in theaforementioned paper. The crossover frequency may be controlled by thevolume of the air chamber II in its relation to the throat impedance.

The design illustrated assumes the choice of a large diaphragmtransducer, but obviously by lengthening the horn to produce a smallerthroat the horn may be fed by a small diaphragn i. The horn may be usedas a low frequency unit and supplemented by smaller speakers operatingat higher frequency ranges, or be operated as discussed above with asingle diaphragm for the two frequency ranges.

The design data in the'table shows an effective mouth area of 5760square inches, whereas the front panel I (Fig. 1) plus the actual mouthsMA and Me possess a combined area of only 2740 square inches or lessthan 'half the effective mouth area. In the absence of the walls andfloor extending out from the mouths, the effective mouth area would beso reduced that its equivalent diameter would be of the order of onehalfwave-length at a frequency of about 150 cycles.

In the present invention, the presence of the walls and floor are takenadvantage of to increase the effective mouth opening, whereby a slowlyflared horn may develop its full capability in the low frequencyregister without the necessity of exceedingly large horn or bafllestructures.

Any material possessing suitable rigidity may be used for the baiiles.Molded material, plywood, and the like which have been used in otherhorn and directional baffle structures may, of course, be used here.

The terms horn and directional baflle have been used synonymously, bothbeing used to designate flaring horn structures, the term horn beinggenerally used to designate one h'avlnga small throat adapted to load asmall diaphragm, and directional baflle designating a large throat hornadapted to load a large conical diaphragm. For a given frequencyperformance, the only difference is the length since the mouth openingand the rate of flare must be the same in each case.

Obviously the speaker just described may be fitted with outer sidewalls. to take the place of the walls of the room. If such sidewallsextend out from the mouths to form reflectors, the

same performance will be obtained as if the speaker shown were operatedin the corner of a room. In such event a sufiicient outward extensionwould be of the order of the width of the actual mouth opening. Thus aspeaker as described is adapted for more versatile service and need notbe limited to its room corner environment; it might, for example, beoperated in the open, or on a theater stage, by fitting it withartificial walls.

I claim:

1. In a loud speaker horn adapted to be located in a corner formed byand to cooperate with three mutually perpendicular walls so that saidwalls together with the horn structure form a .part of the horn thecombination of, a pair of non-parallel baffles perpendicular to one ofsaid surfaces, a panel extending between said baffles at their mostwidely separated edges and transversely of the plane bisecting the angleformed by the other two of said mutually perpendicular walls, a coverfitting upon said panel and parallel to said first surface and baffles,said cover extending sidewardly therefrom to abut the two side walls,said baffles being more closely spaced to said side walls at their mostclosely spaced edges than at their most widely spaced edges by an amountsubstantially of the rate of one-half for each increment of length alongthe side walls of x/ 18 where M is the longest wave length to betransmitted by said horn, and means within the enclosure formed betweenthe pair of baffles forming an elongated horn section, said section atits large end communicating with the air column formed by the bafflesand the side wall surfaces and at its small end communicating with asound source.

2. In a horn type loud speaker wherein three mutually perpendicular wallsurfaces cooperate to form a part of the speaker which comprises, asubstantially rectangular panel extending substantially normal to aplane bisecting the angle formed by two of said wall surfaces and to thethird wall surface, said panel being of a width to provide open spacesbetween its side edges and the two wall surfaces, baiiles with edgesterminating in spaced relation with each other and the said wallsurfaces, a cover member in abutting relation with said baffies, saidpanel and said two wall surfaces whereby a horn section is formedbetween said wall surfaces and said baffles and whereby said hornsection is divided by the enclosure formed by said baflles, panel andcover member, and additional baiiles within the speaker enclosureforming a further length of tapered horn terminating at its large end inthe divided horn section formed by the mutually perpendicular wallsurfaces and the first mentioned baflles and at its small endterminating in an air chamber adapted to be closed by a vibratingdiaphragm sound source, two of said additional bafiles being arrangedwithin the speaker enclosure and forming with the first mentionedbaffles a pair of horn sections opening into the first mentioned hornsections.

3. In a horn type loud speaker wherein three mutually perpendicular wallsurfaces cooperate to form a part of the speaker which comprises, asubstantially rectangular panel extending subtantially normal to a planebisecting the angle formed by two of said wall surfaces and to the thirdwall surface, said panel being of a width to provide open spaces betweenits side edges and the two wall surfaces, baflles with edges abuttingsaid side edges and other edges in abutting relation with said thirdwall surface and extending convergingly from said panel toward thecorner formed by said two surfaces, said baffles terminating in spacedrelation with each other and the said wall surfaces, a cover member inabutting relation with said bailles, said panel and said two wallsurfaces whereby a horn section is formed between said wall surfaces andsaid baflles and whereby said horn section is divided by the enclosureformed by said baffles, panel and cover member, and additional bailleswithin the speaker enclosure forming a further length of tapered hornterminating at its large end in the divided horn section formed by themutually perpendicular wall surfaces and the first mentioned bafiles andat its small end terminating in an air chamber adapted to be closed by avibrating diaphragm sound source, two of. said additional baffiesextending substantially parallel with said first mentioned baflles andforming therewith a pair of horn sections opening divergingly into thefirst mentioned horn sections.

4. In a horn type loud speaker wherein three mutually perpendicular wallsurfaces cooperate to form a part of the speaker which comprises, asubstantially rectangular panel extending substantially normal to aplane bisecting the angle formed by two of said wall surfaces and to thethird wall surface, said panel being of a width to provide open spacesbetween its side edges and the two wall surfaces, bafiles with edgesabutting said side edges and other edges in abutting relation with saidthird wall surface and extending convergingly from said panel toward thecorner formed by said two surfaces, said baffles terminating in spacedrelation with each other and the said wall surfaces, a cover member inabutting relation with said baflles, said panel and said two wallsurfaces whereby a horn section is formed between said wall surfaces andsaid bellies and whereby said horn section is divided by the enclosureformed by said baflies, panel and cover member, and additional bail'ieswithin the speaker enclosure forming a further length of tapered hornterminating at its large end in. the divided horn section formed by themutually perpendicular wall surfaces and the first mentioned baiiies andat its small end terminating in an air chamber adapted to be closed by avibrating diaphragm sound source, said additonal baiiies being arrangedin pairs extending in opposite directions and forming successivediverging pairs of horn sections, the outermost of said horn sectionsopening into the first mentioned horn sections.

5. In a loud speaker horn wherein three mutually perpendicular wallsurfaces cooperate to form a part of the horn the combination of, asubstantially rectangular panel extending substantially perpendicular toa plane bisecting the angle formed by two of said wall surfaces and tothe third wall surface, said panel being of a width to provide openspaces between its side edges and the two wall surfaces, baflies withedges abutting said side edges and other edges in abutting relation withsaid third wall surface and extending convergingly from said paneltoward the corner formed by said two wall surfaces, said baiilesterminating in spaced relation to each other and the said wall surfaces,a cover member in abutting relation with said baifles, said panel andsaid two wall surfaces whereby a horn section is formed between saidwall surfaces and said battles and whereby said horn section is dividedby the enclosure formed by said baiiles, panel, and cover member, andadditional bailles within said enclosure forming a further length oftapered horn terminating at its large end in said divided horn sectionand terminating at its small end in an aperture adapted to be closed bya vibrating diaphragm sound source.

6. In a loud speaker horn wherein three mutually perpendicular wallsurfaces cooperate to form a part of the horn the combination of, asubstantially rectangular panel extending substantially perpendicular toa plane bisecting the angle formed by two of said wall surfaces and tothe abutting third wall surface, said panel being of a width to provideopen spaces between its side edges and the two wall surfaces, baiileswith edges abutting said side edges and other edges in abutting relationwith said third wall surface and extending convergingly from said paneltoward the corner formed by said two wall surfaces, said bafliesterminating in spaced relation to' each other and the said wallsurfaces, 9. cover member in abutting relation with said baffies, saidpanel and said two wall surfaces whereby a horn section is formedbetween said wall surfaces and said baffles and whereby said hornsection is divided by the enclosure formed by said baflies, panel, andcover member, and additional baflles within said enclosure forming afurther length of tapered horn terminating at its large end in saiddivided horn section and terminated at its small end in an aperturedmember, and a vibrating diaphragm sound source closing said aperture.

7. In a loud speaker wherein three mutually perpendicular surfacescooperate to form a part of the horn the combination of, a substantiallyrectangular panel extending substantially perpendicular to a planebisecting the angle formed by two of said wall surfaces and to the thirdwall surface, said panel being of a width to provide open spaces betweenits side edges and the two wall surfaces, baiiies with edges abuttingsaidv side edges and other edges in abutting relation with said thirdwall surface and extending convergingly from said panel toward thecorner formed by said two wall surfaces, said bames terminating inspaced relation to each other and the said wall surfaces, 2. covermember in abutting relation with said bafile, said panel and said twowall surfaces whereby a horn section is formed between said wallsurfaces and said bailie and whereby said horn section is divided by theenclmure formed by said bailles, panel and cover member, additionalbaflles within the said enclosure forming a further length of taperedhorn terminating at its large end in said divided horn section andterminated at its small end by an apertured member arranged andconstructed for the aperture therein to be closed by a vibratingdiaphragm sound source, and battles diverging from said panel toward thecorner and extending between and forming a passage diverging toward thefree edges of the converging baflles.

PAUL W. KLIPSCH.

Patent No. 2,310,243 Granted February 9, 1943 PAUL W. KLIPSCH The aboveentitled patent was extended October 2, 1951, under the provisions ofthe Act of June 30, 1950, for 6 years and 120 days from the expirationof the original term thereof.

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